Overall Evaluation of the Effect of Residual Stress Induced by Shot Peening in the Improvement of Fatigue Fracture Resistance for Metallic Materials

Before 1980s,the circular suspension spring in automobile subjected to torsion fatigue load,under the cyclic normal tensile stresses,the majority of fatigue fracture occurred was in normal tensile fracture mode（NTFM）and the fracture surface was under 45°diagonal.Because there exists the interaction between the residual stresses induced by shot peening and the applied cyclic normal tensile stresses in NTFM,which represents as＂stress strengthening mechanism＂,shot peening technology could be used for improving the fatigue fracture resistance（FFR）of springs.However,since 1990s up to date,in addition to regular NTFM,the fatigue fractures occurred of peened springs from time to time are in longitudinal shear fracture mode（LSFM）or transverse shear fracture mode（TSFM）with the increase of applied cyclic shear stresses,which leads to a remarkable decrease of FFR.However,LSFM/TSFM can be avoided effectively by means of shot peening treatment again on the peened springs.The phenomena have been rarely happened before.At present there are few literatures concerning this problem.Based upon the results of force analysis of a spring,there is no interaction between the residual stresses by shot peening and the applied cyclic shear stresses in shear fracture.This;means that the effect of＂stress strengthening mechanism＂for improving the FFR of LSFM/TSFM is disappeared basically.During shot peening,however,both of residual stress and cyclic plastic deformed microstructure are induced synchronously like＂twins＂in the surface layer of a spring.It has been found for the first time by means of force analysis and experimental results that the modified microstructure in the＂twins＂as a＂structure strengthening mechanism＂can improve the FFR of LSFM/TSFM.At the same time,it is;also shown that the optimum technology of shot peening strengthening must have both＂stress strengthening mechanism＂and＂structure strengthening mechanism＂simultaneously so that the FFR of both NTFM and LSFM/TSFM can be improved by shot peening.

Characteristics Study on Bi-Pb Based Alloys Quenched from Melt

Three different bismuth-lead systems namely, Wood＇s alloy （Bi50Pb25Sn12.5Cd12.5）, Newton＇s alloy （Bi50Pb31.2Sn18.8） and Rose＇s alloy （B50Pb28Sn22）, with one used as fusible alloys were quenched from melt by melt spinning technique. Thermal analysis, structure and mechanical properties of all alloys have been studied and analyzed. From X-ray diffraction analysis, an intermetallic compound phase, designated Pb7Bi3 is detected. The formation of an intermetallic compound phase causes a pronounced increase in the electrical resistivity. The Wood＇s alloy containing-cadmium exhibits mechanical properties superior to both the Newton＇s and Rose＇s alloys. The presence of cadmium in Wood＇s alloy decreases its melting point. Wood＇s alloy has better properties, which make it useful in various applications such as in protection shields for radiotherapy, locking of mechanical devices and welding at low temperature.

A Study of Structure, Thermal and Mechanical Properties of Free Machining Al-Zn-Sn-Bi Alloys Rapidly Solidified from Molten State

The objective of our study is to investigate the effect of rapid solidification technology using melt spun process from melt on environmentally free machining Al-0.1Zn alloys with tin-bismuth as free machining constituents. The main purpose of rapid solidification from melt is to have a high strength and thermal stability. Structural and thermal properties have been investigated by x-ray diffraction (XRD), scanning electron microscope (SEM) and differential scanning calorimetry (DSC) techniques. Tensile test machine is used to study the mechanical properties such as ultimate tensile strength, elastic constants, yield strength and critical shear stress for free machining alloys. We find?the best free machining aluminum alloy that has excellent machinability qualities is Al-0.1Zn-0.5Sn-0.54Bi melt spun alloy because it offers excellent mechanical properties. The highest values of tensile strength (431.5 MPa), yield strength (393.9 MPa), fracture strength (431.6 Mpa), toughness (15.8 × 106?J/m3) generated from Al-0.1Zn-0.5Sn-0.54Bi alloy to meet the needs of free machining aluminum alloy applications.

Microstructures and Mechanical Properties of Al-Zn-Sn Bearing Alloys for High Performance Applications

The mechanical behavior and indentation creep of Al-20 wt% Zn bearing alloy has been modified with adding 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt% Sn. These bearing alloys were prepared by melt spinning technique. The scanning electron microscopy (SEM) was used to study the morphology of the melt spun alloys and x-ray diffractometer (XRD) for the identification of the phases pre- sent in these melt-spun bearing alloys. The results show that the structure of Al80-x-Zn20-SnX (X = 0.2%, 0.5%, 1% and 1.5%) bearing alloys is characterized by the presence of α-Al of FCC structure and SnZn intermetallic compound of anorthic structure. The Al-20Zn-1.5Sn has a smaller crystallite size and grain size as indicated from X-ray and SEM analysis respectively, which leading to the enhancement of the mechanical properties. The mechanical properties and indentation creep of these bearing alloys were studied by tensile test machine and vickers indentation testing at room temperature, respectively. The Al-20Zn-1.5Sn has higher hardness value and creep resistance than other alloys. This was attributed to the strengthen effect of Sn as a strong solid solution element in Al-matrix. The stress exponent values in the range 2.4 - 4.2 indicate that the grain boundary sliding is the possible mechanism during room temperature creep deformation of melt-spun Al-Zn-Sn bearing alloys.

Structural, Magnetic and Dielectric Properties of Fe-Co Co-Doped Ba_0.9Sr_0.1TiO₃Prepared by Sol Gel Technique

The structural, dielectric and magnetic properties of pure and Fe-Co co-doped Ba0.9Sr0.1TiO3, (Ba(1-x)SrxTiO3, where (x = 0.10) and (Ba0.9Sr0.1Ti(1-x-y)FexCoyO3), where (x = 0.1, y = 0) and (x = 0 and y = 0.10) and (x = 0.5, y = 0.5) in powder form, abbreviated as (BST) and (BST10FO), (BST10CO) and (BST5F5CO), respectively were prepared by a modified sol gel technique. Crystallization, surface morphology and electrical behavior of BST are improved by Fe3+ and Co2+ ions with optimized grain size. Phase identification by using X-ray diffraction and surface morphology will be studied by using transmission electron microscope (TEM) and scanning electron microscope imaging (SEM). Phase identification by using X-ray diffraction and surface morphology evaluation by using transmission electron microscope (TEM) and scanning electron microscope imaging (SEM) will be studied. The nano-scale presence and the formation of the tetragonal perovskite phase as well as the crystallinity were detected using the mentioned techniques. The dielectric properties of the prepared samples have been investigated as a function of temperature and frequency. The dielectric measurements are carried out in the frequency range of 42 Hz - 1 MHz, at temperature ranging between 25°C and 250°C. The results showed an abrupt decrease in the dielectric permittivity by increasing the frequency range. The magnetic hysteresis loop confirmed enhancement in the magnetization properties by co-doping with Fe3+-Co2+ ions. An increase in the saturation of the magnetization at room temperature was detected by decreasing the crystallite sizes of the prepared samples.

Dielectric and Magnetic Properties of Nano-Structure BiFeO<SUB>3</SUB>Doped with Different Concentrations of Co Ions Prepared by Sol-Gel Method

BiFe1-xCoxO3 (x = 0, 0.03, 0.05 and 0.1) symbolic as (BFO, BF3CO, BF5CO and BF10CO) in powder form has been prepared by sol-gel technique using ethylenediamine tetraacetic acid (EDTA) as a chelating agent. X-ray diffraction (XRD) and FTIR analysis showed rhombohedra distorted BiFeO3 structure with compressive lattice distortion induced by the Co substitution at Fe sites. The transmission electron microscope (TEM) shows irregular particles. The additive of cobalt oxide has led to grains refining giving the following crystallite sizes of 18 nm for BF5Co. The scanning electron microscope (SEM) study reveals that the samples morphology shows relatively uniform grain size distribution. The dielectric properties of BiFeO3 nano-particles in the frequency range of 1 up to 5 MHz at RT revealed that the A.C. conductivity of the prepared samples reaches its maximum value in BF5CO. By decreasing BiFeO3 particle size as a result of doping with different Co ion concentrations, an enhancement in magnetization and a simultaneous suppression in current leakage occurred. The remnant magnetization Mr of BiFe1-xCoxO3 (x = 0, 0.03, 0.05, 0.1) ceramics significantly enhanced, which provides potential applications in information storage.